Components such as aerofoils for gas turbines engines are typically super plastically formed in a die cavity which is defined by two opposing dies. Each die has a forming surface 1 which shapes the material into the desired component form (as shown in FIG. 1a) and an opposing rear surface 2 (as shown in FIG. 1b).
Cavities 3 are typically formed into the rear surface 2 of the die in order to reduce the thermal mass of the die which, in turn, reduces cooling of the furnace upon introduction of the die and reduces heat retention by the die after removal from the furnace.
The cavities 3 in the rear surface 2 of the die are typically separated by a plurality of walls 4 (as shown in FIG. 1d). The walls help increase the strength of the die to allow it to withstand press forces. The walls typically differ in width/thickness, in some cases by up to 50%. The thickness of the die at the base 5 of the cavities 4 also differs (as shown in FIG. 1c). The walls are constructed so that several different component dies take up a similar space and will therefore fit a single press without changing the position or stroke of the press.
Although not explicitly shown in the FIGS. 1a-d, additional pockets or projections may be formed into the rear surface of the die to act as fixture/guide features to ensure accurate location of the die within the furnace and/or against the opposing die(s).
The variation in the thickness of the die/walls leads to thermal and contraction stresses which can reduce the life of the die and, over time and cycles lead to distortion of the die which, in turn can lead to undesirable variation in the shape of the cast or forged component.
There is a desire for a die, for use in die casting or hot forging, which has an increased life and reduces undesirable variation in the shape of the cast component and thus reduces the need for/extent of post-casting or post-forging machining.